214 



ARION HORTENSIS. 



Parasites and Enemies. — Probably almost equally liable with other 

 species to destruction and annoyance by the ordinary enemies and para- 

 sites of slug-life ; there is, however, little published evidence on the subject, 

 although it has been observed that the Blindworni {Angnisfragilis) which 

 greedily devours AgrioUnmx agrestis, would not eat the present species, 

 possibly on account of its very leathery skin and sticky mucus. A further 

 protective feature was suggested by the late Mr. Sherriff Tye, who remarked 

 upon the very remarkable likeness existing between this species and 

 portions of the bloom-sheaths of the Black Poplar {Populus nigra), a pro- 

 tective resemblance which is operative at a period of the slug's greatest 

 activity, and when its natural enemies, the thrushes, having young to 

 provide for, are more industrious than usual in searching them out. 



Fossil. — Kennard and Woodward record calcareous particles, believed 

 to be the ^'cstigial shells of this species, from a holocene deposit on the 

 face of a clialk escarpment at Exedown, near Wrotham, in West Kent. 



Variation. — The variation in this species runs in two chief lines, 

 exemplified by the typical form and the large variety subfuscus. 



Fdrussac has remarked on the circumstance that succeeding generations 

 do not invariably reproduce the variation prevalent during the preceding 

 year, and Dr. Scharff has observed the same peculiarity in the locality at 

 Killakee in the Dublin Mountains, the large brown variety subfusca being 

 exclusively found there in February, 1891, while in May of the previous 

 year, in precisely the same spot all the specimens found were of the grey or 

 typical form. In connection with this point, it may be remarked that 

 Mr. Gain during his feeding experiments found a constant and marked 

 difference as regards food in the likes and dislikes of the ordinary form 

 and the var. subfusca. 



Dr. Simroth is of opinion that the light-coloured variations are the eff'ect 

 of warmth, while the darker-hued individuals owe their shade of colouring 

 to cold ; but this alone does not universally apply. 



The grey variety is, however, found most prevalent in the open country, 

 while the brown or yellowish variety are more numerous in other localities, 

 though in gardens they may frequently be found in the closest association. 



The Avion cottianus Poll, from 

 Piedmont, and Avion elxmgatus 

 Collinge from Somerset, do not 

 seem to diff'er materially from 

 the typical form of the present 

 species. 



Prof Cockerell, in The Concho- 

 logist, 1891, p. ;U, described an 

 immature Avion, found at Acton, 

 Middlesex, which he named var. 

 (dbipes. It was described as a 

 form of Avion hovtensis with 

 white foot and colourless slime. 



Mr. B. Tomlin, in The Journal 

 of Conchology, April 1887, re- 

 cords two albine specimens found 

 at Hele, near Ilfracombe, in 

 company with albine forms of 

 other species, but he does not further allude to or describe them. 



Fig. 228. Fig. 229. 



Fig. 228,— Proximal end of the Sexual system of 

 Arion Itoriemis, enlarged (after Pollonera). 



Fig. 220. — Proximal end of the Sexual system of 

 Arion cottiaints, enlarged (after Polloneia). 



